Method of reconstructing successive scans of a bar code

ABSTRACT

A method of reconstructing successive scans of bar codes having a plurality of dark elements separated from light elements, comprising the steps of: performing a first scan of the bar code thereby determining the position and the width of the elements in the first scan with respect to an absolute reference position; calculating the position which the elements in the first scan will take with respect to the absolute reference position in a subsequent scan; making a second scan of the bar code thereby determining the position and the width of the elements in the second scan with respect to the absolute reference position; carrying out a correspondence search step for finding at least one reference element for the first scan and one reference element for the second scan, which have substantially the same position with respect to the absolute reference position and substantially the same width; and combining the elements in the first scan with the elements in the second scan, generating a reconstructed scan.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/316,119filed May 20, 1999 now U.S. Pat. No. 6,394,352. The invention relates toa method of reconstructing successive scans of a bar code.

BACKGROUND OF THE INVENTION

As is known, bar codes (FIG. 2) are optical codes containing codedinformation made up of a plurality of rectangular elements (bars) havinga dark color (normally black) separated by light elements (spaces,normally white).

Reading devices for the said bar codes usually comprise an illuminationdevice (e.g. a laser beam source) adapted to send an optical readingbeam which moves along a scanning path intersecting the bar code andalso comprise a sensor (e.g. a photodiode) which receives part of thediffused light from the portion of the scanning path illuminated by thelaser spot. The sensor, in response to the radiation falling on it as aresult of scanning a bar code, outputs an alternating electric signalhaving a wave shape which is modulated by the succession of light anddark elements in the bar code. As is known, light is absorbed by thebars and reflected by the spaces, so that the signal generated by aspace has a high value owing to the large amount of incident radiationon the sensor, whereas the signal generated by a bar has a low valueowing to the small amount of incident radiation on the sensor.

In this manner, a signal generated by scanning the bar code issuccessively binarised and has a two-level wave shape which representsthe elements of the bar code and comprises a first high level whenscanning a space and a second low level when scanning a bar.

Normally bar codes are examined in a scanning direction which does notcoincide with the longitudinal axis of the code. The scanning directionis therefore usually at an angle to the longitudinal axis of the barcode. More particularly, when this angle exceeds a threshold value αmax(FIG. 2), a subset of the code elements are scanned and the binarisedsignal, which relates to a partial scan of the bar code, comprises asubset of the code elements.

In known devices also, relative movement occurs between the illuminationdevice and the objects bearing the bar codes. For example theillumination device is fixed and the objects move with respect to theillumination device at a constant speed, when carried by a movingdevice.

For this reason, successive partial scans normally relate to scanning ofvarious adjacent subgroups in the bar code.

Some known reconstruction devices are adapted to put together successivepartial scans of the same code, made in different positions, in order toreconstruct and decode the bar code.

Reconstruction devices of this kind, which put together those elementsof a partial scan which have a given —inclination with respect to thelongitudinal axis of the bar code, effect an omnidirectional readout ofthe code.

SUMMARY OF THE INVENTION

The object of the invention is to provide a method of reconstructingsuccessive partial scans of a bar code, featuring a particularlyefficient omnidirectional reading of the code. Furthermore, object ofthe invention is to provide a method of reconstructing successivepartial scans so as to efficiently manipulate the successive partialscans.

This object is achieved by the invention, which relates to a method ofreconstructing successive scans of a bar code comprising a plurality ofelements, said elements having a first and a second reflectivity andbeing represented by a position with respect to a reference position andby a width, characterized by the steps of: performing a first scan ofthe bar code, determining the position and the width of the elements inthe first scan with respect to an absolute reference position;calculating the position which said elements in said first scan willtake respect to said absolute reference position in a subsequent scan;making a second scan of the bar code, determining the position and thewidth of the elements in said second scan with respect to said absolutereference position; carrying out a correspondence search step to find atleast one reference element in said first scan and one reference elementin said second scan which both have substantially the same position withrespect to said absolute reference and substantially the same width; andcombining the elements in said first scan with t elements in said secondscan so as to generate a reconstructed scan.

More particularly, said correspondence search step is followed by acoupling check step for checking that at least a predetermined number ofelements in said first scan and said second scan have substantially thesame position with respect to the absolute reference position andsubstantially the same width.

More particularly, the coupling check step is carried out by comparingat least one minimum defined set of elements in said first scan with aminimum defined set of elements in said second scan.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings which illustrate a non-limitative embodiment thereof and inwhich:

FIG. 1 is a diagram of a device for reading bar codes, using the methodaccording to the invention;

FIG. 2 shows a bar code;

FIG. 3a is a logic block diagram illustrating a sequence of steps of themethod according to the invention;

FIG. 3b shows a detail of a block in FIG. 3a;

FIG. 3c shows a detail of a block in FIG. 3b;

FIG. 3d shows a detail of a block in FIG. 3b;

FIG. 3e shows a detail of a block in FIG. 3b;

FIG. 3f shows a detail of a block in FIG. 3b;

FIG. 3g shows a detail of a block in FIG. 3f;

FIGS. 3h and 3 i show details of a block in FIG. 3f;

FIG. 3j shows a detail of a block in FIG. 3f;

FIG. 3l shows a detail of a block in FIG. 3f;

FIGS. 3m and 3 n show a different embodiment with respect to FIGS. 3hand 3 i;

FIGS. 4a and 4 b show the time function of an electric-signal relatingto scanning of a bar code;

FIG. 5 illustrates scanning of the bar code of FIG. 2;

FIG. 6 shows a data structure constructed according to the invention;

FIG. 7 shows the time function of signals obtained by the methodaccording to the invention;

FIG. 8 shows a step of the method according to the invention and

FIG. 9 shows a subsequent step of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, reference number 1 indicates as a whole a bar code readingdevice comprising a reading head 5 facing a conveyor belt 6 and adaptedto pick out objects 7 (e.g. packets) disposed on the belt 6 and movablein a rectilinear direction D at a constant speed with respect to thereading head 5. One surface 7 a of each object 7 facing the reading head5 bears one or more optical codes 8, more particularly bar codes ofknown kind (FIG. 2). Each bar code is made up of a plurality ofrectangular portions (bars) having varying reflectivity, moreparticularly dark (normally black) portions separated by light portions(spaces, normally white). Different dark and light portions (bars andspaces) can have different widths.

The light and dark portions of the code, i.e. the bars and spaces, arethe elements of the bar code. In the following description, therefore, acode “element” will mean a bar or a space of the code.

Adjacent elements of the code together form a character of the code, towhich coded information is associated.

More particularly the bar code, near a first end portion thereof, has aplurality of elements which together define a code starting character,hereinafter called a START pattern (FIG. 2). Furthermore, the bar code,near a second-end portion thereof, has a plurality of elements whichtogether define an end-of-code character, hereinafter called a STOPpattern. The beginning-of-code and end-of-code characters, i.e. theSTART pattern and the STOP pattern, define the so-called “synchronismcharacters” of the code.

The reading head 5 comprises a known illumination device 17 (e.g.comprising a laser source 17 a and a rotating prismatic mirror 17 badapted to reflect the laser beam produced by the source 17 a), fordirecting a laser scanning beam F on to the optical codes 8 and scanningthe codes 8.

More particularly the laser beam F moves in a substantially inclinedplane and intersects the belt 6 and the objects thereon along a scanningpath L on which the laser spot moves from a beginning-of-scanningposition Li to an end-of-scanning position Lf.

The reading head 5 also comprises a sensor 20 (e.g. a photodiode)associated with an optical acquisition and focusing system 21(diagrammatically represented) for picking up the diffused lightradiation R in order to generate an output analog signal S(t) having anintensity proportional to the brightness of the portion of the path Lwhich is being scanned at that moment. The analog signal S(t) is fedto-an electronic unit 22 which processes the analog signal S(t)according to the invention. The unit 22 is also adapted to pick up thecoded information associated with the code.

Of course, the reading device described with reference to FIG. 1 is oneexample of the various reading devices which could be used inassociation with the method according to the invention; the device 1could be of a different kind and could e.g. comprise a lamp or LEDs forilluminating the bar codes, or a telecamera or a CCD for picking up agrey-level bidimensional image of the bar codes and of the successiveprocessing devices, which likewise output a signal S(t) having anintensity proportional to the brightness of a portion of a scanned barcode.

FIG. 3a is a general block diagram of the operating cycle of anelectronic processing unit 22.

More particularly FIG. 3a proceeds from a starting block (START) to ablock 100 which acquires the analog signal S(t) generated by the sensor20 after a complete scan of scanning path L. A “complete scan” means ascan in which the laser spot moves from the beginning-of-scanningposition Li to the end-of-scanning position Lf.

The analog signal S(t) typically has an initial portion corresponding toscanning the beginning-of-scanning position Li (FIG. 1), a final portioncorresponding to scanning the end-of-scanning position Lf and anintermediate section which, corresponding to a scanned bar code,comprises an alternating section (shown in FIG. 4a) formed by a sequenceof zones P having a high amplitude (peaks) separated by zones V of lowamplitude (valleys).

In the wave form of the alternating section of the signal S(t), a peak Prepresents a space whereas a valley V represents a bar.

The analog signal S(t) is then binarised in the block 100 and,corresponding to an alternating section thereof, outputs a signal Sd(t)having two levels (shown in FIG. 4b) comprising a first high level HI onscanning a space and a second low level LO on scanning a bar. The highlevels HI and low levels LO of the signal Sd(t) are joined bysubstantially vertical transition fronts which separate thedifferent-level portions of the signal Sd(t) and represent theseparation zone between two different elements (bar-space) of the code.

The wave form of the binarised signal Sd(t) is situated on a time axishaving its origin (time to) at the instant when scanning begins, i.e.the instant at which the laser spot illuminates thebeginning-of-scanning position Li.

The beginning-of-scanning position Li is an absolute spatial referenceto which the positions of the bar code elements are referred andconsequently the instant to is taken as an absolute time reference withrespect to which the positions in time of the code elements representedby the signal Sd(t) are measured.

More particularly the time Tp measured between the time origin to and aninstant ti when a digitized signal front Sd(t) is present, representsthe time distance between the bar code element following the consideredfront and the absolute reference (to).

The time interval Tp represents the position of a bar code element withrespect to the beginning-of-scanning position.

The time width Tc of the high-level portion HI and/or low-level portionLO of the digitized signal Sd(t) represents the width of a bar codeelement. For this reason, each bar code element is represented in thesignal Sd(t) by a time interval Tp which represents the position of thebar code element with respect to the absolute reference (time toequivalent to the beginning-of-scanning position Li) and by a timeinterval Tc which represents the width of the code element.

In the subsequent description, for simplicity, reference I will be madeto the position of the code element, meaning by this term the timedistance Tp thereof, whereas by “width of the code element” the timeinterval Tc is meant.

In the following description also, the term FRAME will mean a set ofcode elements as represented by the digitized signal Sd(t).

In other words, each FRAME comprises a plurality of positions and widthsrepresenting the elements of the scanned bar code.

A FRAME, for example, can be represented by a table TABF (FIG. 9) inwhich:

a first line comprises a number of cells each of which contains theposition, with respect to the absolute reference to (time Tp), of anelement of the FRAME and therefore represents the position of a bar codeelement; and

a second line comprises a plurality of cells each of which contains thewidth (time Tc) of the corresponding FRAME element and consequentlyrepresents the width of a bar code element.

In the following description, the term CLUSTER means a set of FRAMESgrouped together by methods described hereinafter. In practice, eachCLUSTER represents a storage area in which the FRAMES relating to agiven bar code are stored, in the same order as the FRAMES themselvesare acquired during successive scans as explained hereinafter.

In similar manner to the FRAMES, the CLUSTER elements are representede.g. by a table TABC (FIG. 9) in which:

a first row comprises a plurality of cells each of which contains theposition, with respect to the absolute reference to (time Tp), of anelement of the CLUSTER and therefore represents the position of a barcode element grouped in the CLUSTER; and

a second row comprises a plurality of cells each of which contains thewidth (time Tc) of the corresponding element of the CLUSTER andtherefore represents the width of a bar code element grouped in theCLUSTER.

Tables TABC and TABF can be scanned by respective pointers i And j whichare able to select pairs of cells (one from the first row and anotherfrom the second row) which define a bar code element through itsposition and its width.

When a number of optical codes or a number of portions of optical codesare illuminated by a single scan, the signal Sd(t) comprises a set ofdistinct different FRAMES F1, F2, . . . Fn.

A FRAME contains all the elements of a bar code only when the scanoccurs along a line between the longitudinal axis H of the code and aline L′ (FIG. 2) at an inclination less than or equal to αmax withrespect to the axis H.

However, the objects 7 and the optical codes 8 thereon have an arbitraryrelative arrangement with respect to the scanning path L. Consequentlythe scanning line normally intersects only a part of the bar code.

For this reason, each FRAME normally relates to scanning of a subgroupof the bar code elements (not of the entire bar code). Consequently eachFRAME relates to a partial scan and represents the cited subgroup ofelements.

Furthermore, owing to the motion of the objects 7 with respect to thereading head 5, successive partial scans L1, L2, . . . (FIG. 5)intersect adjacent portions of the code and produce successive FRAMESwhich relate to different subgroups of elements. Also, the inventionrelates to a method of reconstructing successive partial scans of barcodes starting from a general signal representing the code elements. Itdoes not matter how the signal was generated or processed.

As will be clearer in the following description, the successive FRAMESrelating to scanning of the same code are grouped in a respectiveCLUSTER which can be individually selected on the basis of the valuetaken by a pointer i.

Each CLUSTER is also marked by a first index called STATUS, whichindicates the state of the CLUSTER; more particularly the index can takethree values corresponding to three different situations:

STATUS=0—the associated CLUSTER is empty, i.e. is not associated withany active data structure in which FRAMES can be grouped;

STATUS=1—the associated CLUSTER contains a frame whereby a synchronismcharacter, i.e. a START pattern or a STOP pattern, has been recognizedfor a first time; and

STATUS=2—the CLUSTER contains at least two FRAMES whereby synchronismcharacters have been recognized.

In the following description, STATUS 1 and STATUS 2 will be calledactive states, whereas STATUS 0 will be called inactive state. Ofcourse, when the algorithm is activated, the STATUS index of all theCLUSTERS will be zero. Subsequently the STATUS index of the CLUSTERS ismodified (transferred to one of the two active states or set at zero)depending on the result of checks made on the CLUSTER itself or on theresult of attempts to couple each CLUSTER to the extracted FRAMES asdescribed—in detail. Consequently, active CLUSTERS and inactive CLUSTERSwill generally be present at every moment.

Each CLUSTER is also marked by a second index called NOMATCH whichrepresents the number of failed attempts made to associate additionalFRAMES to the same CLUSTER.

The block 100 is followed by a block 110 for canceling the contents i ofa counter in accordance with the logic operation i=0.

The block 110 is followed by a block 120 which selects the i^(th)CLUSTER and checks the status of the first STATUS index associated withthis i^(th) CLUSTER. More particularly the block 120 checks whether theSTATUS index of the i^(th) CLUSTER is an active state, i.e.:

CLUSTER(i), STATUS=1; or

CLUSTER(i), STATUS=2

In the case where the check by block 120 gives a positive result (i.e.the i^(th) CLUSTER examined is in the active state), a block 130 isselected; otherwise (i^(th) CLUSTER inactive) the block 120 is followedby a block 140.

The block 130 re-selects the i^(th) CLUSTER and checks the value of thesecond NOMATCH index; more particularly if the NOMATCH index is equal toor above a threshold value MAX-NOMATCH, i.e. if at least MAX-NOMATCHfailed attempts have been made to associate the i^(th) CLUSTER withadditional FRAMES, block 130 will select a block 150 for forcing to zerothe first STATUS index of the i CLUSTER which at present is active,i.e., CLUSTER(i), STATUS=0.

In other words, active CLUSTERS for which at least MAX-NOMATCH failedattempts have been made to associate them with new FRAMES aretransferred to the inactive state, i.e. cancelled and made available forstoring FRAME elements which cannot be associated with active CLUSTERS.

The block 150 is followed by block 140.

The block 140 is adapted to examine the current value i of the counter;If the value is below the maximum number of CLUSTERS present in thememory (i<MAXIMUM NUMBER OF CLUSTERS) the block 140 is followed by ablock 160 which increases by one unit the contents i of the counter, bythe logic operation i=i+1, and a return is made from block 160 to block120.

If block 140 detects that the contents i of the counter is equal to thenumber of CLUSTERS present in the memory (i=MAXIMUM NUMBER OF CLUSTER)block 140 is followed by block 170.

The preceding operations have the combined result of scanning the set ofall the CLUSTERS present in the memory and the following operations areperformed for each scanned CLUSTER:

if the CLUSTER is marked by an inactive state index (STATUS=0), theCLUSTER is not modified (i.e. no type of operation is performed); and

if the CLUSTER is marked by an active state index (STATUS=1, 2), thenumber of failed attempts to associate the said CLUSTER with additionalframes is checked and, if the threshold value MAX-NOMATCH is exceeded,the CLUSTER is put in the inactive state by forcing to zero the STATUSindex.

The block 170 is adapted in known manner to select a single FRAME Fifrom the signal Sd(t) relating to a complete scan.

The block 170 is followed by a block 180 adapted to count the number Nfof elements of the FRAME Fi previously selected, i.e. the number of barcode elements represented by the FRAME. If the number Nf is above aminimum number of elements defining a threshold value, the block 180 isfollowed by a block 190, otherwise the block 180 is followed by a block200. The block 190 (described in detail hereinafter) selected when theFRAME Fi comprises a number of elements above the minimum number ofelements is adapted to process the FRAME, i.e. is adapted to try toassociate the FRAME Fi with each active CLUSTER. The block 190 is in anycase followed by the block 200, which checks whether the FRAME Fi underexamination is the last FRAME contained in the scan detected by theblock 100. If not, a return is made from block 200 to block 170 in orderto select another FRAME Fi+1, or otherwise (after examination of theFRAMES in the scan) a return is made from block 200 to block 100 inorder to acquire another scan. In the other scan, of course, the objects7 will be in a different position from the preceding scan andconsequently different portions of the bar code will be scanned andFRAMES will be detected relating to partial scans of the codes made indifferent successive positions from the positions in the preceding scan.

FIG. 3b gives a detailed view of the block 190 adapted to process theFRAME Fi extracted from the block 170. The process consists inattempting to associate the FRAME Fi with all the active CLUSTERSpresent in the memory adapted to select a first CLUSTER. The block 191is followed by a block 192 which checks whether the selected CLUSTER isthe last CLUSTER present in the memory.

More particularly, the block 190 comprises a block 191 adapted to selecta first CLUSTER. The block 191 is followed by a block 192 which checkswhether the selected CLUSTER is the last CLUSTER present in the memory.If not so (other CLUSTERS are present in the memory) the block 190selects a block 193, otherwise (after examination of the CLUSTERSpresent in the memory) the block 192 selects a block 194.

More particularly, the block 190 comprises a block 192 adapted to selecta first CLUSTER. The block 192 is followed by a block 193 which checkswhether the selected CLUSTER is an active CLUSTER; if so (the selectedCLUSTER is active) the block 193 is followed by a block 195, otherwise(the selected CLUSTER is inactive) a block 191 is selected, which checkswhether the selected CLUSTER is the last CLUSTER present in the memory.If not so (other CLUSTERS are present in the memory) the block 191returns to block 192, otherwise (after examination of the memory) theblock 191 returns to block 192, otherwise (after examination of theCLUSTERS present in the memory) the block 191 selects a block 194.

The block 193 checks whether the selected CLUSTER is an active CLUSTER;if so (the selected CLUSTER is active) the block 193 is followed by ablock 195, otherwise (the selected CLUSTER is inactive) a return is madefrom block 193 to block 191.

The combined results of the previously-described operation is to scanall the CLUSTERS (active and inactive) and select the active CLUSTERSonly. In the case of each selected active CLUSTER, an attempt is made toassociate the FRAME Fi as described hereinafter.

Initially, the block 195 (described in detail hereinafter) checkswhether the FRAME Fi and the selected CLUSTER intersect, i.e. whetherthe FRAME and the CLUSTER comprise elements which have comparablepositions when superposed.

If the check of the block 195 gives a negative result (the FRAME Fi andthe CLUSTER do not intersect) a return is made from block 195 to block191. Otherwise (the FRAME Fi and the CLUSTER intersect and can becombined) the block 195 is followed by a block 196.

The block 196 modifies a state index of the FRAME, by putting it in astate indicating the use made of the FRAME. Indeed this use is madesubsequently during the next attempt to combine the FRAME Fi with thevarious active CLUSTERS.

The block 196 is followed by a block 197 which checks whether the FRAMEFi has already been decoded; if not (no attempt has yet been made todecode the FRAME) the block 197 is followed by a block 197 a whichattempts this decoding. Otherwise (the FRAME has already been decoded)the block 197 is followed by a block 198. The fact that the FRAME hasbeen successfully decoded in block 197 a means that this FRAME comprisesall the elements of the bar code; in that case it is of courseunnecessary to reconstruct the successive partial scans. The decodedcode is therefore transmitted to the exterior of the unit 22.

The block 198 (described in detail hereinafter) tries to combine theFRAME Fi with a first active CLUSTER; if the attempt has a negativeresult, the contents of a counter measuring the NOMATCH number of failedcombination attempts made by the CLUSTER is incremented by one unit andthe block 198 is followed by the block 191 for selecting another activeCLUSTER and repeating the effort to combine the same FRAME Fi with theadditional CLUSTER. The block 198 (described in detail hereinafter)tries to combine the FRAME Fi with a first active CLUSTER; if theattempt has a negative result, the contents of a counter measuring theNOMATCH number of failed combination attempts made by the CLUSTER isincremented by one unit and the block 198 is followed by the block 191and, if this was not the last cluster, by the block 192 for selecting.

If the combination process in the block 198 has given a positive result,the block 198 is followed by a block 198 a which tries to decode theCLUSTER to which the FRAME Fi has been successfully added. If theCLUSTER is successfully decoded, the decoded code is transmitted to theexterior of the unit 22. The block 198 a is likewise followed by theblock 191.

The block 194 checks the value of the state index of the FRAME Fiindicative of its use. If the index indicates that the FRAME Fi has beensubjected to a combination attempt with at least one active CLUSTER, atransition is made from block 194 to block 200 (FIG. 3a) for selecting(block 170) an additional FRAME Fi+1 which will be subjected to theoperations in block 190 described with reference to FIG. 3b. If thestate index of the FRAME indicates that the FRAME Fi has not yet beensubjected to a combination attempt, the block 194 is followed by a block194 a (described in detail hereinafter) which initializes a CLUSTER byinserting the FRAME Fi into it. The block 194 a is likewise followed bythe block 200.

FIG. 3c shows details of the block 195 which checks whether the FRAME Fiand the selected CLUSTER intersect and are therefore superposable.

The block 195 comprises a first block 195 a which checks whether theposition Tf1 (FIG. 7) of the last element in the FRAME with respect tothe absolute reference (the beginning-of-scanning position correspondingto the time to) is lower than the position TCf of the first element ofthe CLUSTER with respect to the absolute reference, i.e., Tfl<TCf (1).

If the inequality (1) hereinbefore gives a positive result, the CLUSTERand the FRAME are recognized as non-superposable and a return is madefrom block 195 a to block 191. If the inequality (1) hereinbefore givesa negative result, the block 195 a is followed by a block 195 b.

The block 195 b checks whether the position TFf of the first element inthe FRAME with respect to the absolute reference is higher than theposition TCl of the last element in the CLUSTER with respect to theabsolute reference, i.e.: TCl<TFf (2).

If the inequality (2) hereinbefore gives a positive result, the CLUSTERand the FRAME are recognized as non-superposable and a return is madefrom block 195 b to block 191. If both the inequalities (1) and (2)hereinbefore give a negative result, the CLUSTER and the FRAME arerecognized as superposable and the block 195 b is followed by the block196. FIG. 7 illustrates the case where both inequalities have given anegative result, when as can be seen the CLUSTER and the FRAME have asuperposed zone SZ (indicated by shading) containing elements havingcomparable positions in the CLUSTER and in the FRAME.

FIG. 3d illustrates the blocks 197 a or 198 a, which try to decode theFRAME (or the CLUSTER).

The block 197 a, 198 a comprises an initial block 201 which checkswhether the length of the FRAME (or the CLUSTER) is acceptable for a barcode, i.e. whether it contains a number of elements compatible with abar code.

If not (the FRAME or CLUSTER has a length incompatible with the lengthof a bar code) the block 201 is followed by the block 198 (or 191),otherwise the block 201 is followed by a block 202. The block 202 triesto decode the FRAME (or the CLUSTER) in a manner known per se, e.g. asdescribed in U.S. Pat. Nos. 3,723,710, 3,761,685 or 3,838,251. Decodingthe frame in block 202 is sufficient in those fortunate cases where theentire code is read from the first scans. In such cases it is impossibleto couple the FRAME to the relevant CLUSTER a second time (as explainedin detail hereinafter with reference to block 400 in FIG. 3g) andconsequently the process does not go via the block 198 a (FIG. 3b) fordecoding the CLUSTER. If no decoding occurs the block 202 is followed bythe block 198 (or 191), or otherwise (the FRAME or CLUSTER is decodedsuccessfully) the block 202 is followed by a block 203. The block 203transmits the contents of decoding the FRAME (or CLUSTER) to theexterior of the unit 22, thus decoding the bar code. The block 203 isfollowed by a block 204 which indicates that the FRAME (or CLUSTER) hasbeen decoded. The block 204 is followed by block 198 (or 191). Althoughthe FRAME (or CLUSTER) has been decoded, efforts are still made toassociate the FRAME with other CLUSTERS, since the wrong code may havebeen decoded. Subsequently and in known manner, the true decoding of thecode is chosen from among all decodings made.

FIG. 3e illustrates block 194 a, which initializes a CLUSTER. Block 194a comprises an initial block 206 for checking whether there is asynchronism character in the FRAME under examination. If the check byblock 206 is positive, a transition is made to a block 207, otherwisethe block 206 is followed by block 200.

The block 207 copies all the elements of the FRAME inside a CLUSTER bytransferring the position and width of all the FRAME elements to theCLUSTER.

The block 207 is followed by a block 208 which sets the state index ofthe CLUSTER at 1, i.e. STATUS=1 in that the CLUSTER now contains a FRAMEcontaining a synchronism character. The block 208 is followed by theblock 200.

In other words, if the FRAME has not been used in any active CLUSTER, anattempt at initialization is made by copying the FRAME in a new CLUSTER,but only if the FRAME has a synchronism character.

FIG. 3f gives a detailed view of the block 198 which tries to associatea FRAME Fi with an active CLUSTER.

The block 198 comprises an initial block 300 which controls the stateindex, variable between 1 and 2, of the CLUSTER. The CLUSTERS examinedby block 300 are only active CLUSTERS, i.e. undoubtedly contain at leastone FRAME in which a synchronism character is present. The block 300selects a block 310 if a STATUS of 1 is detected, or a block 320 if aSTATUS of 2 is detected.

Basically the block 310 is selected on examination of a CLUSTER whichcontains a single FRAME in which a synchronism character is present.

The block 310 checks whether the FRAME under examination contains asecond synchronism character. If the check is negative, the block 310 isfollowed by a block 330 which cancels the CLUSTER by setting its stateat zero, i.e. the CLUSTER is made inactive and the possiblereconstruction is blocked. The block 330 is also followed by the block191.

In the case of a positive check by the block 310, i.e. if the FRAMEcontains a second synchronism character, reconstruction begins.Therefore, reconstruction begins only after detection of two successiveFRAMES each containing a synchronism character.

To this end the block 310 is followed by a block 340 (described indetail hereinafter) which checks for correspondence between the FRAMEand the CLUSTER in order to check whether the FRAME and the CLUSTERbelong to the same code.

The block 340 selects a block 345 if the check gives a negative result(FRAME and CLUSTER not aligned) or a block 350 if the check is positive(FRAME and CLUSTER in line), thus setting the STATUS of the CLUSTER at2. The block 345 increases the counter defining the NOMATCH number byone unit; this block is in fact selected after a failed attempt whensearching for correspondence between a FRAME and a CLUSTER. The block345 is then followed by the block 191.

The block 340 then calculates the distance between the synchronismcharacter of the FRAME and the corresponding synchronism character ofthe CLUSTER.

In this connection reference should be made to FIG. 3g, whichillustrates the block 340 which calculates the distance Δ-position aftersuccessfully checking for correspondence between the FRAME and theCLUSTER, in order to check whether the FRAME and the CLUSTER relate toscanning of the same code.

The block 340 comprises an initial block 400 which checks whether thenumber of elements in the FRAME is greater than the number of elementsin the CLUSTER. If this is not so, an error situation is detected andthe block 400 is followed by block 345 and 191; otherwise the block 400is followed by block 410. Of course, in the fortunate case in which theentire bar code has already been read in the preceding scan and thepresent scan also relates to all the elements of the code, the checkmade in block 400 will prevent coupling between the actual FRAME and theCLUSTER and the situation will be as described hereinbefore withreference to block 197 a in FIG. 3b.

The block 410 calculates the number f of code elements which aresuperposed in the FRAME and in the CLUSTER, i.e. which have the sameposition with respect to the absolute reference and the same width, bymaking the comparison (FIG. 8) starting from the first element of theFRAME and from the first element of the CLUSTER (corresponding to theleft or FORWARD).

The block 410 is followed by a block 420 which calculates the number rof elements which are superposed in the FRAME and in the CLUSTER, i.e.which have the same position with respect to the absolute reference andthe same width, starting the comparison from the last element of theFRAME and from the last element of the CLUSTER (corresponding to theright or REVERSE).

Referring to FIG. 8, the CLUSTER contains the code elements detected inthe scan marked L1, whereas the FRAME contains the code elements foundby the scan marked L2.

The block 420 is followed by a block 430 which checks whether the numberr is equal to the number f. If the numbers r and f are equal, anuncertainty situation is detected (the number of superposable elementson the right corresponds to the number of superposable elements on theleft) and consequently the code is not reconstructed. The block 430 isfollowed by blocks 345 and 191. If the numbers r and f are different,the block 430 is followed by a block 440 which checks whether the numberr or the number f is different from zero. If at least one of the saidnumbers is equal to zero, a non-correspondence situation is detected andconsequently the code is not reconstructed. Blocks 430 and 440 arefollowed by blocks 345 and 191. If either the number r or the number fare different from zero, a block 450 is selected which checks whetherthe number f is greater than the number r. If the number f is greaterthan the number r a block 460 f is selected, otherwise (f is less thanr) a block 460 r is selected.

The block 460 f checks whether the number f of superposable elementsstarting from the left is greater than a threshold value MINMATCH; if fis less than the threshold (i.e. when there are a limited number ofelements which are superposed in the FRAME and in the CLUSTER), an erroris detected, reconstruction does not begin and consequently blocks 345and 191 are selected. If f is greater than the MINMATCH threshold (i.e.if there are a sufficient number of superposed elements in the FRAME andin the CLUSTER) the block 460 f selects a block 470 f which stores thesuperposition condition starting from the left (or FORWARD direction) ofthe bar code with respect to the reading head. The block 470 f isfollowed by a block 480 f which calculates the value Δ-position as thedifference between the position of the first element in the FRAME andthe position of the first element in the CLUSTER (see FIG. 7).

Reconstruction of the code therefore begins and the block 480 f isfollowed by a block 350 (FIGS. 3f and 3 g) which puts the STATUS indexat two (STATUS=2) indicating the beginning of reconstruction. Thesituation in fact means that two successive superposable FRAMES havebeen detected and both have a synchronism code; the term Δ-position hasalso been calculated on the basis of these two first FRAMES.

The block 460 r checks whether the number r of superposable elementsstarting from the right is greater than a threshold value MINMATCH. If ris less than the threshold (i.e. if there are a limited number ofcorresponding elements in the FRAME and in the CLUSTER) an error isdetected, reconstruction does not begin and the blocks 345 and 191 areselected. If r is above the MINMATCH threshold (i.e. when there is asufficient number of superposed elements in the FRAME and in theCLUSTER) the block 460 r selects a block 470 r which stores thesuperposition condition starting from the right (BACKWARDS or REVERSEdirection) of the bar code with respect to the reading head. The block470 r is followed by a block 480 r which calculates the value Δ-positionas the difference between the position of the last element in the FRAMEand the position of the last element in the CLUSTER.

Reconstruction of the code therefore begins and the block 480 r is alsofollowed by the block 350 which sets the state index at two.

Returning to FIG. 3f, the block 350 which, as already stated, sets thefirst STATUS index of the CLUSTER at 2 indicating the beginning ofreconstruction, is followed by a block 355 which associates the FRAMEwith the CLUSTER by copying the FRAME elements in the CLUSTER.

The block 355 is followed by a block 380 which recalculates the positionof the CLUSTER by disposing it in the position provided for thesubsequent scan (due to the movement of the conveyor belt 6 (FIG. 1) andbased on the measured displacement of the CLUSTER with respect to thejust-associated FRAME. The block 380 (described in detail in FIG. 31)applies the Δ-position displacement to all elements of the CLUSTER, i.e.a new position is calculated for each element of the CLUSTER by summingthe Δ-position term at the present position. For each element in theCLUSTER, therefore, the block 380 makes the following transformation:

NEW POSITION OF CLUSTER ELEMENT=PRESENT POSITION OF CLUSTERELEMENT+Δ-position

To this end, note that the belt 6 moves at a substantially constantspeed (e.g. 3 meters per second) with respect to the reading head; themirror 17 b also rotates at high speed, e.g. sufficient for 1000 scansper second. The time between one scan and the next is very short, equalto {fraction (1/1000)} of a second in the present case. During this timeinterval the speed of the belt is practically constant, in thatsubstantial variations in speed would require very high acceleration (ofthe order of several tens of g) which are obviously unobtainable orunimaginable in the case of a conveyor-belt device.

Consequently the position to be taken by the CLUSTER in order to becomparable with a FRAME detected in a subsequent scan is approximatedwith high accuracy by the block 380 (FIG. 3l), which subjects therelevant elements in the CLUSTER to a final scan after making adisplacement (Δ-position) which is estimated on the assumption of aconstant velocity between the last scan contained in the CLUSTER and thesubsequent scan which will give rise to the next FRAME.

The block 380 is then followed by the block 198 a.

The block 320 (described in detail hereinafter) reached whenreconstruction is begun, STATUS=2, checks whether the FRAME Fi and theCLUSTER analyzed by block 300 can be associated. The CLUSTER taking partin the operations of block 320 is a CLUSTER which contains two FRAMESeach comprising a synchronism character; the block 320 is normallyselected during the third or fourth scan of the bar code.

If the association attempted by block 320 is unsuccessful, block 320 isfollowed by a block 360 which increases by one unit the counter whichdefines the number NOMATCH; the block 360 is then followed by the block191.

If the association attempt by block 320 is successful, the block 320 isfollowed by a block 365 (described in detail hereinafter) which correctsthe calculation of the distance Δ-position between the FRAME and theCLUSTER˜ previously calculated in block 340 (FIG. 3g).

Block 365 is followed by a block 370 (similar to block 355) which, afterthe operations performed by block 320, associates the new FRAME elementsin the CLUSTER. The operations of block 370 will be described in detailhereinafter.

Blocks 355 and 370 are followed by block 380, which in turn is followedby block 198 a.

FIGS. 3h and 3 i illustrate details of the block 320, which tries toassociate the FRAME Fi with the CLUSTER under examination

The block 320 comprises an initial block 500 (FIG. 3h) which checkswhether the bar code has made a FORWARD movement (block 460 f, FIG. 3g)or a REVERSE movement (block 460 r, FIG. 3g) with respect to the readinghead. In the first case (FORWARD movement) a block 510 is selected andin the second case (REVERSE movement) a block 520 b is selected (FIG.3i)

Block 510 selects the last-but-one element in the CLUSTER, defined bythe value ic of a pointer in Table TABC and the last-but-one element ofthe FRAME, defined by the value jn of a pointer in Table TABF (FIG. 9).In the description hereinafter, for brevity, the term “element ic in theCLUSTER” is used to identify the element in the CLUSTER which is definedby the pointer value ic and “element jn in the FRAME” is used toidentify the element of the FRAME which is defined by the pointer valuejn.

The block 510 is followed by a block 520 which checks whether theposition of element ic of the CLUSTER with respect to the absolutereference is approximately equal to the position of the element jn ofthe FRAME with respect to the same absolute reference.

In the negative case (the positions of ic and jn do not coincide) theblock 520 is followed by the block 530. Otherwise (the positions of icand jn substantially coincide) the block 520 is followed by a block 540.

The block 530 checks whether the position of element ic in the CLUSTERis higher than the position of element jn in the FRAME.

If so (the position of element ic in the CLUSTER is higher than theposition of the element jn in the FRAME) a block 555 is selected;otherwise a block 550 is selected. FIG. 9 illustrates the case regardingselection of the block 550 when the position of element jn of the FRAMEis higher than the position of element ic of the CLUSTER.

The block 550 decrements by one unit the value of jn, i.e. performs theoperation jn=jn−1, in order to select a FRAME element having a lowerposition than the preceding one. Correspondingly, the block 555decrements by unity the value of ic, i.e. performs the operation ic−1,in order to select a CLUSTER element having a lower position than thepreceding one.

Blocks 555 and 550 are both followed by a block 560 which checks whetherthe values ic and jn (previously modified by the respective blocks 555and 550) are now below a threshold value MINMATCH, i.e.:

jn<MINMATCH

or

ic<MINMATCH

If at least one of the inequalities hereinbefore is satisfied, block 560is followed by block 360 (FIGS. 3h and 3 f) which detects an errorsituation and increases the number NOMATCH which describes the number offailed attempts at coupling between CLUSTERS and FRAMES.

If neither inequality of block 560 is satisfied, a return is made fromblock 560 to block 320, which re-checks the position of the elements icof the CLUSTER and jn of the FRAME; the check is made by a differentelement of the CLUSTER or FRAME from the element used in the precedingcheck step.

The block 540 is selected when the elements ic and jn of the CLUSTER andof the FRAME have substantially the same position. In the example inFIG. 9 this happens when the pointer jn moves from the position from theright to the position on the left at which jn corresponds to an element(a space in the illustrated example) in the FRAME having the sameposition with respect to the absolute reference as the element (space)in the CLUSTER marked by ic.

Block 540 performs the following operations:

select a plurality of CLUSTER elements starting from the element markedic in the REVERSE direction towards elements (ic−1, ic−2, . . . ic−n)preceding the said element ic. “Preceding elements” with respect to agiven element mean elements having a lower position than the givenelement.

select a plurality of FRAME elements starting from the element marked jnin the REVERSE direction towards elements (jn−1, jn−2, . . . jn−m)preceding the considered element; and

calculate the number A(ic,jn) of superposable elements by comparing atleast MINMATCH selected elements in the CLUSTER and in the FRAME,starting from ic and jn. “Superposable elements” means a continuoussequence of elements of the FRAME and of the CLUSTER in which eachelement of the FRAME of the sequence corresponds to a respective elementof the CLUSTER having the same position and the same width.

Block 540 is followed by a block 580 which checks whether the numberA(ic, jn) is greater than the number MINMATCH, i.e.:

A(ic,jn)>MINMATCH

If so (A(ic,jn)>MINMATCH) the block 580 is followed by blocks 365 and370 (FIG. 3f), otherwise (A(ic,jn)<MINMATCH) block 580 is followed byblock 530 for a new attempt to check superposability starting from aFRAME element ic or a CLUSTER element jn adjoining the element lastconsidered, since the check for identity of position made in block 520is only approximate and the calculation and check of the number ofsuperposable elements (based on blocks 540 and 580) may have been madeon bar code elements which are distant by only one position.

If so, i.e. if the check shows that the FRAME and CLUSTER can besuccessfully coupled, a move is made (FIG. 3f) to block 365 (whichrecalculates the value Δ-position) and to block 370 (FIG. 3f) whichcopies the FRAME elements following jn in the CLUSTER starting from theelement ic.

The operations illustrated with reference to FIG. 3i are similar tothose illustrated in FIG. 3h, but in this case the operations relate tothe REVERSE direction of motion whereas the operations illustrated withreference to FIG. 3h are for the FORWARD direction of advance.

Block 520 b (FIG. 3i) sets the values of ic and jn at zero, i.e.ic=jn=0.

Block 520 b is followed by a block 590 which checks whether the positionof the CLUSTER element ic detected with respect to the absolutereference is approximately the same as the position of the FRAME elementjn detected with respect to the absolute reference.

If not (i.e. if the positions of the elements associated with ic and jndo not coincide) block 590 is followed by block 600, otherwise (theposition of the elements associated with ic and jn substantiallycoincide) block 590 is followed by a block 610.

Block 600 checks whether the position of element ic in the CLUSTER ishigher than the position of the FRAME element jn. If so (position ofCLUSTER element ic>position of FRAME element jn), a block 620 isselected, otherwise, a block 630 is selected.

The block 620 increases the value of jn by one unit, i.e. performs theoperation jn=jn+1, in order to select a FRAME element having a higherposition than the preceding one. Similarly block 630 increases the valueof ic by one unit, i.e. performs the operation ic=ic+1, in order toselect a CLUSTER element having a higher position than the precedingone.

Blocks 620 and 630 are both followed by a block 640 which checks whetherthe values of ic and jn (previously modified by the blocks 630 and 620respectively) are now greater than the number of elements in the CLUSTERminus a threshold value MINMATCH, i.e.:

ic>number of elements in the CLUSTER−MINMATCH

or

jn>number of elements in the CLUSTER−MINMATCH.

If at least one of the inequalities hereinbefore is satisfied, block 640is followed by block 360 (FIGS. 3i and 3 f) which detects an errorsituation and increases the NOMATCH number, which describes the numberof failed attempts at coupling CLUSTER and FRAME.

If none of the inequalities is satisfied in block 640, block 640 isfollowed by block 590 which re-checks the position of the elementsassociated with ic and jn. The check is made on a different CLUSTERelement or FRAME element from that used in the preceding check step.

The block 610 is selected when the elements associated with ic and jnhave substantially the same position and performs the followingoperations:

it selects a plurality of CLUSTER elements starting from the elementmarked ic and in the FORWARD direction towards elements (ic+1, ic+2, . .. ic+n) which follow the last element ic. “Elements which follow a givenelement” mean elements having a higher position than the given element.

it selects a plurality of FRAME elements starting from the elementmarked jn and in the FORWARD direction towards elements (jn+1, jn+2, . .. jn+m) following the last element jn and

it calculates the number A(ic,jn) of superposable elements by comparingat least MINMATCH selected elements of the CLUSTER and the FRAME.

Block 610 is followed by a block 660 which checks whether the numberA(ic,jn) is greater than the number MINMATCH, i.e.:

A(ic,jn)>MINMATCH

If so, A(ic,jn)>MINMATCH, the block 660 is followed by blocks 365 and370; if not (A(ic,jn)<MINMATCH), block 660 is followed by block 600.

In the positive case, i.e. where the FRAME and CLUSTER can besuccessfully coupled, a move is made to block 365 (FIG. 3f) whichrecalculates the value Δ-position and to the block 370 and the FRAMEelements preceding jn are copied in the CLUSTER, starting from theelement ic.

Element ic is therefore a reference element with respect to which theCLUSTER and the FRAME are aligned. Block 370 also carries out a“junction” step between the FRAME and the CLUSTER in which all the FRAMEelements disposed on a given side with respect to the reference elementare copied in the CLUSTER. More particularly in the FORWARD case (FIG.3h) from the reference element (i.e. towards elements having a higherposition) the FRAME elements are selected and copied in the CLUSTER,whereas in the BACKWARD direction from the reference point (i.e. towardselements having a lower position) the CLUSTER elements are retained.

The operations performed by block 320 define a correspondence searchstep in which a selection is made (blocks 510 and 520 a) of an element(denoted by the pointer value ic, ic−1, ic+1) for beginning a check ofthe CLUSTER; a selection is made (blocks 510 and 520 a) of a check startelement (denoted by pointer value jn) of the FRAME and a correspondingcheck step is carried out (blocks 520 and 590) to check whether theposition of the check start element in the CLUSTER with respect to theabsolute reference is approximately the same as the position of thecheck start element of the FRAME with respect to the absolute reference.

If the correspondence check step gives a negative result, an iterativemodification step is carried out (by blocks 530, 555, 559, 560; 600,620, 630, 640) in order to select subsequent CLUSTER or FRAME elementsadjoining the check start element. The iterative modification step iscarried out by other CLUSTER or FRAME elements until the correspondencecheck step arrives at a positive result (output to blocks 540 and 610).In such cases, a possible coupling between FRAME and CLUSTER isinitially detected. Initially the coupling is detected in the case of asingle element of the FRAME or the CLUSTER. In order however torecognize the coupling with greater reliability, a series of furtheroperations are performed in the method according to the invention,including the following:

selecting (blocks 540, 610) a plurality of CLUSTER elements startingfrom the reference element which satisfies the correspondence check stepin a predetermined direction (i.e. in the REVERSE or the FORWARDdirection), starting from the reference element towards elements remotefrom the reference element;

selecting (blocks 540, 610) a plurality of FRAME elements starting fromthe reference element (jn) which satisfies the correspondence check stepand in a predetermined direction (the said REVERSE and FORWARDdirections) starting from the reference element towards elements remotefrom the reference element;

calculating (blocks 540, 610) the number of superposable elements amongthose selected in the CLUSTER and in the FRAME and

detecting (blocks 580 and 660) that the correspondence search step hasgiven a positive result when the number of superposable elements has apredetermined relation to (more particularly is greater than) thereference MINMATCH.

In this manner, coupling between FRAME and CLUSTER is recognized withgreater reliability in that FRAME elements and CLUSTER elements arecompared together.

Note that the correspondence search operations start from thelast-but-one element of the FRAME or the CLUSTER. The last FRAME orCLUSTER element is not selected, since it may provide information whichis insufficiently reliable, e.g. because of noise.

The last-but-one element is chosen because (see FIG. 8, scan L2) thelast element may be only partly crossed by the scanning line, with theresult that its width is uncertain.

In this way, the reliability of the correspondence search algorithm isimproved.

FIG. 3j shows the block 365, which recalculates the distance Δ-positionbetween the FRAME and the CLUSTER. The distance Δ-position is calculatedfor the first time by block 340. More particularly, the block 365recalculates the distance Δ-position as the difference between theposition of FRAME element jn and CLUSTER element ic.

As can be seen, therefore, the term Δ-position is initially calculated afirst time in block 340 at the beginning of the coupling operations andis successively refined by calculation in block 365.

FIG. 3m illustrates a variant of that described with reference to FIG.3h. For simplicity, only the parts differing from those previouslyillustrated will be described.

In the variant shown, block 540 comprises a block 540 a which performsthe following operations:

it selects a plurality of CLUSTER elements starting from the elementdenoted by ic in the backward (REVERSE) direction towards elements(ic−1, ic−2, . . . ic−n) preceding element ic. “Elements preceding agiven element” means elements having a lower position than this element.

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the backward (REVERSE) direction towards element (jn−1,jn−2, . . . jn−m) preceding this element and

it calculates the number A(ic,jn) of superposable elements by comparingat least MINMATCH selected elements of the CLUSTER and of the FRAMEstarting from ic and jn. “Superposable elements” means a continuoussequence of elements of the FRAME and of the CLUSTER in which each FRAMEelement of the sequence corresponds to a respective CLUSTER elementhaving the same position and the same width.

The block 540 a is followed by block 540 b, which performs the followingoperations:

it selects a plurality of CLUSTER elements starting from the elementdenoted by ic−1 in the backward (REVERSE) direction towards elements(ic−2, ic−3, . . . ic−n) preceding element ic−1;

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the backward (REVERSE) direction towards elements(jn−1, jn−2, . . . jn−m) preceding this element and

it calculates the number B(ic−1,jn) of superposable elements bycomparing at least MINMATCH selected elements of the CLUSTER and of theFRAME.

The block 540 b is followed by the block 540 c which performs thefollowing operations:

It selects a plurality of CLUSTER elements starting from the elementdenoted by ic+1 in the backward (REVERSE) direction towards elements(ic, ic−i, . . . ic−n) preceding element ic+1;

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the backward (REVERSE) direction towards elements(jn−1, jn−2, . . . jn−m) preceding this element and

it calculates the number C(ic+i,jn) of superposable elements bycomparing at least MINMATCH selected elements of the CLUSTER and of theFRAME.

The block 540 c (the last step in block 540) is followed by a block 570which searches for the largest number Mb among the numbers A(ic,jn),B(ic−1,jn), C(ic+1,jn) which have previously been calculated in blocks540 a, 540 b and 540 c.

The block 570 is followed by a block 580 which checks whether thepreviously-extracted number Mb is greater than a threshold valueMINMATCH; if the check made by block 580 has given a negative result(Mb<MINMATCH) a return is made to block 520; if not (Mb>MINMATCH) a moveis made from block 580 to block 365.

If it is found that the FRAME and CLUSTER have been successfullycoupled, therefore, block 365 (recalculating the value Δ-position) andblock 370 are selected (FIG. 3f), block 370 copying the FRAME elementsfollowing jn in the CLUSTER starting from the element ic, ic+J or ic−idepending on whether the selected greatest number is A(ic,jn),B(ic−1,jn) or C(ic+1,jn).

FIG. 3n shows a variant of that described with reference to FIG. 3i. Forsimplicity, only parts differing from those previously illustrated willbe described.

In the variant shown, block 610 comprises a block 610 a which performsthe following operations:

it selects a plurality of CLUSTER elements starting from the elementdenoted by ic in the FORWARD direction towards elements (ic+1, ic+2, . .. ic+n) following the last element ic. “Elements following a givenelement” means elements having a higher position than the given element.

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the FORWARD direction towards elements (jn+1, jn+2, . .. jn+m) following the last element jn; and

it calculates the number A(ic,jn) of superposable elements by comparingat least MINMATCH selected elements of the CLUSTER and of the FRAME.

The block 610 a is followed by block 610 b which performs the followingoperations:

it selects a plurality of CLUSTER elements starting from the elementdenoted by ic−i in the FORWARD direction towards elements (ic, ic+1, . .. ic+n) following element ic−i;

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the FORWARD direction towards elements (jn+1, jn+2, . .. jn+m) following element jn and

it calculates the number B(ic−1,jn) of superposable elements bycomparing at least MINMATCH selected elements of the CLUSTER and of theFRAME.

The block 610 b is followed by block 610 c which performs the followingoperations:

it selects a plurality of CLUSTER elements starting from the elementdenoted by ic+1 in the FORWARD direction towards elements (ic+2, ic+3, .. . ic+n) following element ic+1;

it selects a plurality of FRAME elements starting from the elementdenoted by jn in the FORWARD direction towards elements (jn+1, jn+2, . .. jn+m) following element jn and

calculates the number C(ic+1,jn) of superposable elements by comparingat least MINMATCH selected elements of the CLUSTER and of the FRAME.

The block 610 is followed by a block 650 which searches for the largestnumber Mf from among the numbers A(ic,jn), B(ic−1,jn), C(ic+1,jn)previously calculated by the blocks 610 a, 610 b and 610 c.

Block 650 is followed by a block 660 which checks, whether the number Mfextracted by the previous block 650 is greater than the number MINMATCH,i.e.: Mf>MINMATCH.

If so (Mf>MINMATCH), block 660 is followed by blocks 365 and 370; if not(Mf>MINMATCH) block 660 is followed by block 600.

In the positive case, i.e. where the FRAME and CLUSTER have beensuccessfully coupled, a move is made to block 365 (FIG. 3f) whichrecalculates the value Δ-position and to block 370, which copies theFRAME elements preceding jn in the CLUSTER starting from element ic,ic+1 or ic−1 depending on whether the selected largest number wasA(ic,jn), B(ic−1,jn) or C(ic+1,jn).

Obviously, numerous modifications and variants can be made to the methoddescribed and illustrated here, all coming within the scope of theinvention as defined in the accompanying claims. In particular it isstressed that the present method, instead of being of the continuouskind and continually scanning and processing the code even aftertransmission of the decoded code (as described with reference to FIG.3d, blocks 203, 204), can comprise interruption of the algorithm,setting the CLUSTER to zero and reactivation starting from block 100only after manual actuation or after recognition of a subsequent code(e.g. after a period of scans without FRAMES). In such cases however itis advisable to insert a check that the number of elements in the FRAMEor CLUSTER is equal to a given number of elements, so as to ensure thatthe code has actually been completely read.

Also the algorithm can be modified by inserting some checks. Inparticular, each CLUSTER can be associated with an additional indicator(a zero scan counter) which is incremented after any scan which does notresult in updating of the CLUSTER. In such cases the reading of the zeroscan counter is checked after every scan (e.g. at the initial block100), if the reading exceeds a given threshold value, the STATUS indexof the CLUSTER is set at zero, thus making the CLUSTER available. Thisoperation, however, is not strictly necessary since scans are rarelywithout elements, owing to the noise which exists even in the intervalsbetween one bar code and the next. The noise however enables CLUSTERS tobe opened and subsequently closed by setting the STATUS index of theCLUSTERS at zero, thus making them available for subsequent scans ofeffective code elements.

What is claimed is:
 1. A method of reconstructing at least one bar code comprising a plurality of elements, comprising the steps of: a) providing a current area; b) providing a plurality of loading areas for storing elements of a bar code under reconstruction; c) performing a scan of said at least one bar code; d) associating a sequence of adjacent bar code elements in said scan with said current area; e) attempting to combine the elements in said current area with the elements stored in each of said loading areas.
 2. The method of claim 1, wherein said step e) of attempting to combine comprises, for each loading area: ea) checking whether at least one element in said current area corresponds to a respective element in said loading area, eb) if said step ea) gives a positive result, storing the elements of said current area different from the elements in said loading area into said loading area.
 3. The method of claim 1, comprising, if said step e) gives a negative result for every loading area, a step f) of storing said elements in said current area into a loading area of said plurality of loading areas having no elements stored therein.
 4. The method of claim 3, comprising the step f1) of checking whether said elements in said current area comprise a synchronism character, and wherein said step f) is only carried out if said elements in said current area comprise a synchronism character.
 5. The method of claim 1, comprising iteratively repeating said steps c) to e).
 6. The method of claim 5, comprising repeating said steps d) and e) for each sequence of adjacent bar code elements in the scan obtained at each execution of said step c).
 7. The method of claim 5, comprising, if an execution of said step e) gives a negative result for every loading area, a step f) of storing said elements in said current area into a loading area of said plurality of loading areas having no elements stored therein.
 8. The method of claim 7, comprising the step f1) of checking whether said elements in said current area comprise a synchronism character, and wherein said step f) is only carried out if said elements in said current area comprise a synchronism character.
 9. The method of claim 5, comprising the steps of b1) associating to each loading area a status index capable of assuming a first value indicating that the loading area has no elements stored therein, and at least one value indicating that the loading area has elements stored therein; g) keeping the value of the status index of each loading area up-to-date after each execution of said step e).
 10. The method of claim 9, wherein said step e) of attempting to combine comprises, for each loading area: e1) checking the value of said status index of the loading area, e2a) if the value of said status index of the loading area has said at least one value indicating that the loading area has elements stored therein, checking whether at least one element in the current area corresponds to a respective element in said loading area, and e3) if said step e2a) gives a positive result, storing the elements of said current area different from the elements in said loading area into said loading area.
 11. The method of claim 9, wherein said step g) comprises, if an execution of said step e) for a loading area gives a negative result, setting said status index to said first value for rendering the loading area available for storing new elements.
 12. The method of claim 9, comprising the steps of ba) associating to each loading area a failed attempts counter, and the steps, repeated for each loading area, of ga) if an execution of said step e) for the loading area gives a negative result, incrementing the value of the failed attempt counter of the loading area, and ha) checking whether said failed attempt counter of the loading area exceeds a predetermined threshold value, and if the result is positive, setting said status index to said first value for rendering the loading area available for storing new elements.
 13. The method of claim 9, wherein said at least one value of said status index indicating that the loading area has elements stored therein comprises: a second value selected from the group consisting of a value indicating that no execution of said step e) gave a positive result for said loading area, and a value indicating that no execution of said step e) occurred for said loading area, and a third value indicating that at least one execution of said step e) gave a positive result for said loading area.
 14. The method of claim 13, wherein said step e) of attempting to combine comprises, for each loading area: e1) checking the value of said status index of the loading area, e2a1) if the value of said status index of the loading area has said second value, checking whether the elements of said current area comprise a synchronism character and whether at least one element of the current area corresponds to a respective element of said loading area, e2a2) if the value of said status index of the loading area has said third value, checking whether at least one element of the current area corresponds to a respective element of said loading area, e3) if a step, selected from the group consisting of said steps e2a1) and e2a2), gives a positive result, storing the elements of said current area different from the elements of said loading area into said loading area.
 15. The method of claim 5, comprising the step d1) of checking whether said sequence of adjacent bar code elements comprises more than a preset minimum number of elements, and wherein said step e) is carried out only if said step d1) gives a positive result.
 16. The method of claim 1, comprising repeating said steps d) and e) for each sequence of adjacent bar code elements in said scan.
 17. The method of claim 16, comprising, if an execution of said step e) gives a negative result for every loading area, a step f) of storing said elements in said current area into a loading area of said plurality of loading areas having no elements stored therein.
 18. The method of claim 17, comprising the step f1) of checking whether said elements in said current area comprise a synchronism character, and wherein said step f) is only carried out if said elements in said current area comprise a synchronism character.
 19. The method of claim 16, comprising the steps of b1) associating to each loading area a status index capable of assuming a first value indicating that the loading area has no elements stored therein, and at least one value indicating that the loading area has elements stored therein; g) keeping the value of the status index of each loading area up-to-date after each execution of said step e).
 20. The method of claim 19, wherein said step e) of attempting to combine comprises, for each loading area: e1) checking the value of said status index of the loading area, e2a) if the value of said status index of the loading area has said at least one value indicating that the loading area has elements stored therein, checking whether at least one element in the current area corresponds to a respective element in said loading area, and e3) if said step e2a) gives a positive result, storing the elements of said current area different from the elements in said loading area into said loading area.
 21. The method of claim 19, wherein said step g) comprises, if an execution of said step e) for a loading area gives a negative result, setting said status index to said first value for rendering the loading area available for storing new elements.
 22. The method of claim 19, comprising the steps of ba) associating to each loading area a failed attempts counter, and the steps, repeated for each loading area, of ga) if an execution of said step e) for the loading area gives a negative result, incrementing the value of the failed attempt counter of the loading area, and ha) checking whether said failed attempt counter of the loading area exceeds a predetermined threshold value, and if the result is positive, setting said status index to said first value for rendering the loading area available for storing new elements.
 23. The method of claim 19, wherein said at least one value of said status index indicating that the loading area has elements stored therein comprises: a second value selected from the group consisting of a value indicating that no execution of said step e) gave a positive result for said loading area, and a value indicating that no execution of said step e) occurred for said loading area, and a third value indicating that at least one execution of said step e) gave a positive result for said loading area.
 24. The method of claim 23, wherein said step e) of attempting to combine comprises, for each loading area: e1) checking the value of said status index of the loading area, e2a1) if the value of said status index of the loading area has said second value, checking whether the elements of said current area comprise a synchronism character and whether at least one element of the current area corresponds to a respective element of said loading area, e2a2) if the value of said status index of the loading area has said third value, checking whether at least one element of the current area corresponds to a respective element of said loading area, e3) if a step, selected from the group consisting of said steps e2a1) and e2a2), gives a positive result, storing the elements of said current area different from the elements of said loading area into said loading area.
 25. The method of claim 16, comprising the step d1) of checking whether said sequence of adjacent bar code elements comprises more than a preset minimum number of elements, and wherein said step e) is carried out only if said step d1) gives a positive result.
 26. A method of reconstructing at least one bar code comprising a plurality of elements, comprising the steps of: a) providing a current area; b) providing at least one loading area for storing elements of a bar code under reconstruction, each loading area having a respective failed attempts counter; c) performing a scan of said at least one bar code; d) associating a sequence of adjacent bar code elements in said scan with said current area; and the steps, repeated for each loading area, of: e) attempting to combine the elements in said current area with the elements stored in said loading area; f) if said step of attempting to combine gives a negative result for said loading area, incrementing the failed attempts counter of said loading area; g) checking whether said failed attempts counter of said loading area exceeds a predetermined threshold value, and h) if the result of said checking step g) is positive, rendering said loading area available for storing new elements.
 27. The method of claim 26, wherein said step e) of attempting to combine comprises: ea) checking whether at least one element in said current area corresponds to a respective element in said loading area, eb) if said step ea) gives a positive result, storing the elements of said current area which are different from the elements of said loading area into said loading area.
 28. The method of claim 26, comprising iteratively repeating said steps c) to h).
 29. The method of claim 28, comprising repeating said steps d) to f) for each sequence of adjacent bar code elements in the scan obtained at each execution of said step c).
 30. The method of claim 28, comprising the step d1) of checking whether said sequence of adjacent bar code elements comprises more than a preset minimum number of elements, and wherein said steps e) to h) are carried out only if said step d1) gives a positive result.
 31. The method of claim 26, wherein said step h) of rendering said loading area available for storing new elements comprises canceling the elements stored in said loading area.
 32. A method of reconstructing at least one bar code comprising a plurality of elements, comprising the steps of: a) providing a current area; b) providing a plurality of loading areas for storing elements of a bar code under reconstruction, each of said loading areas having a failed attempts counter; c) performing a scan of said at least one bar code; d) associating a sequence of adjacent bar code elements in said scan with said current area; and the steps, repeated for each loading area, of: e) attempting to combine the elements in said current area with the elements stored in each of said loading areas; f) if said step of attempting to combine gives a negative result, incrementing the failed attempts counter of the loading area; g) checking whether said failed attempts counter of the loading area exceeds a predetermined threshold value, and h) if the result of said checking step g) is positive, rendering the loading area available for storing new elements. 